Sony Zeiss 24-70mm f/4 ZA OSS Lens Review

bythom sony 24-70 f4

What is It?
The 24-70mm f/4 ZA OSS lens was one of the first zoom lenses for the FE mount, and appeared with the original A7/A7R bodies. It's a small, light lens in its collapsed state, so the combination of an A7 body with the 24-70mm made for a very attractive alternative for full frame enthusiasts who were looking for something less of a neck drag than their full frame DSLRs.

More on that when we get to the performance section, below.

Optical construction is a bit lightweight at 12 elements in 10 groups, though there are five aspherical elements in the mix, indicating that Zeiss is bending the light aggressively to get that svelte size. Up front is a 67mm filter ring, and Sony supplies a modest petal-shaped lens mount that bayonets to the front (and can be reversed on the lens for travel). 

The aperture diaphragm is what is called a circular 7-blade, but on my sample it's decidedly not circular. Apertures go down to f/22, though on the high pixel count A7R bodies you'd be diffraction impacted long before you got there. Minimum focus distance works out to be 0.4m, which puts you at 15". Maximum reproduction ratio is a respectable 1:5. 

Zooming takes about a quarter turn, and there are markings for 24, 35, 50, and 70mm. The optical stabilizer is not state-of-the-art, providing only 3 stops CIPA max. 

As I noted, the lens isn't large or heavy. At 24mm it's just 94.5mm long (3.7"), and the lens weighs 430g, an ounce less than a pound. For a 24-70mm mid-range zoom with a constant aperture, these are very low numbers, which as I wrote, makes the lens seem svelte. 

Source of the review lens: purchased

The 24-70mm f/4 lens retails for US$1200. 

Sony's Web site for the lens

How's it Handle?
The zoom and focus rings on this lens are right next to each other and not distinguished by grip feel (you'll know which one you're turning though, as the focus ring is fly-by-wire slippery smooth, and the zoom ring is stiff). I've accidentally moved the focus ring on this lens, which shouldn't happen. Bad ergonomic design.

This is one of those extend-o-zooms: at 24mm it retains its collapsed size, but it extends out to provide 70mm. I wasn't particularly enamored with the build quality: there appears to be a small amount of wobble to the barrel extension on my sample when I zoom in to 70mm. This did not seem to change the optical characteristics, but it makes me worry about things like how well the weather sealing really is.

Other than that, there's nothing to remark about: the lens has no buttons or additional controls to get in your way.

How's it Perform?
Sharpness: There's mostly not good news here. The lens is what I'd call very good (50mm+)  to excellent (24-35mm) in sharpness in the central region, even wide open, except at 70mm where the center is only good. Stopping down really only helps the telephoto side of the lens, where it gets to very good at f/8 at 70mm.

It's the corners that are the downfall of this lens, particularly at the two zoom extremes. At 24mm, even at f/8 you only get fair corners with clear smearing, while at 70mm you have very weak, even poor corners with clearer smearing. Only in the 35-50mm zone do you get the kind of performance closer to what you'd expect: corners improving to be usable and not very smeared.

The smearing appears to be due to both strong coma/astigmatism and a bit of off centering on my sample. I tried another sample and got something similar, but not biased to one side the same way. I've looked at images from other samples of the lens: smearing is a trait of this lens in the corners, regardless of how good the sample is.

Best performance is really f/5.6 across the board on the wide side, f/8 across the board on the telephoto side. But 24mm and 70mm just don't dial in the corners to the level you'd desire (and expect). Corners are often unusable shooting with this lens. 

Note when I write "corners" I mean the absolute corners. The borders on this lens do a little better, but even there I still see issues.

For a lens labeled "Zeiss," the 24-70mm f/4 just doesn't begin to deliver to expectations.

Linear Distortion: The usual "swing": significant barrel distortion (nearly 4%) at the wide end, significant pincushion distortion (about 3%) at the telephoto end. The "neutral" point is somewhere around 28mm. This distortion is exaggerated at the corners, a small form of mustache-type distortion. The in-camera corrections really only take the distortion down to about a half percent, so it's still visible at the two extremes.

Vignetting: At 24mm you have over two stops of vignetting wide open, and even at f/5.6 you're still about a stop and a half. 70mm starts at about a stop and a half, and gets to my good point by f/5.6, becoming unremarkable at f/8 and beyond. The remaining focal lengths are all about a stop wide open (near my good point) and unremarkable at f/5.6 and beyond. In-camera corrections bring this all down to between a quarter stop (50mm f/8) to one stop (24mm f/4). 

Chromatic Aberration: Other than 24mm and wide open at 70mm, the lateral chromatic aberration on this lens is basically ignorable it's so low (even on the 42mp sensor). At 24mm you're going to often get two pixels of CA, particularly in extreme contrast edges. You'll also get that at 70mm wide open, but stopping down removes that issue at the telephoto end (but not at the wide angle end).

Longitudinal chromatic aberration is slightly present wide open, but negligible in the rest of the aperture range.

Bokeh: Is busy, heavily onion-skinned, with visible colored edges. On my sample, rounded out of focus highlights are clearly badly distorted by the aperture blades. Busy and ugly.

Final Words
This is a tough lens to judge. The reasons to like it are these: significantly smaller, lighter and lower priced than the f/2.8 alternative. Indeed, Sony was crafty with their initial f/4 zoom trio coupled with the first A7 bodies. The smaller size and weight gave Sony an apparent "advantage" over the DSLR systems, and at 24mp the flaws weren't as obvious to most as they are with the 42mp A7R2 and A7R3 models.

Now that we have the f/2.8 zoom trio and high resolution sensors, that advantage seems to be completely gone: Sony's FE lenses with excellent acuity are sizing and weighing up there with the DSLR equivalents, which makes the smaller A7 body size and weight far less relevant. Indeed, the f/2.8 lenses on the A7 bodies tend to feel a bit front-heavy in handling (not so much on the heavier A9). 

I've been using the f/4 zoom trio since the A7rII first appeared, so I have quite a lot of experience with them. Simply put, I know that I sacrifice optical performance for pack size/weight when I use those original f/4 lenses.

I'm actually happy with the results with the 24-70mm f/4 in the mid-range. I'm not sacrificing much performance from 35-50mm, and the border-to-border optics of the lens is quite good in this focal range. Where I feel let down is at 24mm off-center. There is definitely not a Zeiss-like performance as you move away from center, even stopped down. I'm less bothered by the corners at 70mm, as I'm often taking photos at that focal length that actually benefit from pushing the eye to the center (e.g. vignetting and corner background softness); unfortunately, the central region at 70mm needs stopping down to f/8 to get everything the lens can provide. The 24-70mm wouldn't be the lens I'd want to be using for architectural or landscape work at any focal length, though. 

At roughly US$1200, you're making a Faustian bargain here: price, size, and weight are all completely optimized against performance. The 24-70mm f/4 remained in my travel kit for quite some time because I learned where it shines and where to avoid using it, and it kept me small and light when mobile. But it wasn't my favorite lens, and by far. I also now have to ask myself if I'd rather just have the fast 35mm and 50mm primes instead. The 24-105mm f/4 is a far better choice, though it, too, has some issues, and it increases your kit size/weight some. Still, the 24-105mm replaced the 24-70mm in my kit.

The other questions you have to ask yourself are these: can you afford the penalties of the excellent f/2.8 GM? and do you even really need a zoom with this range?

It strikes me that the Loxia 21mm f/2.8, the Sony 35mm f/2.8, one of the many Sony 50mm options, and an 85mm telephoto are way better optically, and perhaps not as much size/weight penalty as you might think while traveling if you just pick two or three. What you lose, of course, is the always-on-the-camera zoom aspect of the 24-70mm. In other words, convenience. 

So, here's the real question: are you going to stick a convenience lens on your Sony A7/A9 body, and if so, how much performance are you willing to give up for that convenience? 

I liked the 24-70mm f/4 at first, but I definitely don't love it now. It gave me a compact travel option for when I want to stay lighter and smaller, but that's about it. These days I've managed to put a full A7R3 kit into a very small sling bag, and the 24-70mm f/4 isn't in that kit, the 24-105mm is. 

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